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A series of small wildfires that broke out along Interstate 80 in Northern California destroyed five homes but was showing little growth, fire officials said Thursday.

The fires broke out Wednesday, the same day that California's fleet of 22 air tankers was grounded after one of the planes crashed while battling a separate wildfire in Yosemite National Park, killing the pilot.

The small fires along Interstate 80 about 40 miles northeast of Sacramento had burned through 420 acres, a slight increase from the previous day, the California Department of Forestry and Fire Protection said. Containment went from 10 to 20 percent.

State fire officials previously reported only one home had been destroyed around the small community of Applegate in Placer County.

It was not immediately clear what caused the fires, but officials said they were looking into the possibility that human activity was to blame.

"We don't know the cause, but any time we have multiple fires that started in the same area along the roadside, that tells us we probably have human activity,'' said Daniel Berlant, a CalFire spokesman.

I-80's eastbound lanes were closed for several hours. A single lane was opened when the blaze was 10 percent contained, and the two remaining eastbound lanes remained closed.

The fire was threatening other homes, at least some of which were under mandatory evacuation orders.

Meanwhile, the wildfire in Yosemite had grown to 252 acres and was 10 percent contained. Some 60 homes in the community of Foresta were under evacuation orders.

Fire officials said the air tanker crash on Tuesday occurred as four CalFire aircraft were fighting the blaze as it climbed a steep canyon wall north of the Merced River.

The body of pilot Geoffrey "Craig'' Hunt was recovered Wednesday.

The department had helicopters, guide planes and aircraft from other agencies to take on the blaze and others in the state, but the S-2T tankers that were grounded indefinitely are considered an essential resource for dealing with wildfires before they spiral out of control.